-LRB- CNN -RRB- -- Many Californians were startled awake Monday night and early Tuesday morning by Amber Alerts that made screeching noises on their cell phones . Some people even took to Twitter to complain .

They better get used to it .

The alerts about a blue Nissan -- possibly carrying Ethan Anderson , 8 , and sister Hannah Anderson , 16 -- were the first sent statewide in California under a new program that sends Amber Alerts about abducted children via text messages to millions of mobile phones . The texts are accompanied by a high-pitched squealing sound to get the phone owner 's attention .

Marc Klaas , whose daughter Polly was kidnapped from her California home in 1993 and later found dead , was an unlikely critic of Monday 's statewide alerts , telling CNN that while the messages were well intended , their rollout was `` pretty abysmal . '' He feared residents might be put off by the harsh noise and opt out of the program .

Cell phones have been receiving Amber Alerts since 2005 under a partnership between the wireless industry , the U.S. Justice Department and the National Center for Missing and Exploited Children . But people had to sign up to receive the alerts -- only about 700,000 did -- and then designate the areas they wanted to get alerts for .

They would then only receive alerts for those chosen areas , regardless of where they were physically located . So you could be from Nebraska but vacationing in Florida , for example , and not get an Amber Alert about an abduction a dozen miles from your Tampa hotel .

That system was replaced on December 31 , 2012 , by the Wireless Emergency Alert program , run by FEMA , which sends free , automatic notifications to almost every phone in the surrounding area or even the state . Cellphone owners now receive Amber Alerts , as well as emergency weather alerts , based on their proximity to the emergency , not the location of their phone number . And people must opt out if they prefer not to get the alerts .

HLN : What you should know about mobile Amber Alerts

The messages are sent over a special wireless carrier channel called Cell Broadcast and are n't affected by congestion that might disrupt regular calls and text messages , according to the National Center for Missing and Exploited Children . About 100 Amber Alerts , sent simultaneously to all compatible mobile devices within range of the cellular towers in the affected area , have been sent nationwide so far under the Wireless Emergency Alert program .

The program was credited with locating an abducted 8-month-old boy in Minnesota in February . A Minneapolis teenager saw an Amber Alert on his phone and called police about a neighbor whose Kia matched the description in the alert . The neighbor was arrested , and the infant was recovered unharmed .

Carriers representing 98 % of all U.S. wireless subscribers are on the new program , and more than 200 models of phones support the alerts , said Brian Josef , an assistant vice president for regulatory affairs at CTIA , the wireless industry trade association .

The alerts `` are absolutely saving lives , '' Josef said .

`` We have stressed that these alerts have been used judiciously , sparingly , '' he added , when asked about irritated reactions to Monday 's Amber Alerts in California . Once phone users understand what it is , `` they appreciate the information , '' he said .

Some older phones , including the iPhone 4 , will not receive the alerts .

People can choose not to hear Amber Alerts by adjusting the notification settings on their phones .

Monday 's alert was the third Amber Alert in California in 2013 to use the new system , although the first two were only broadcast to phones in specific counties .

A massive manhunt was under way Tuesday and Wednesday in California for James DiMaggio , 40 , whom law enforcement authorities describe as a friend of the children 's mother , Christina Anderson .

Launched in Texas in 1996 , Amber Alerts were originally sent out via radio , TV and electronic highway signs as part of the national emergency-alert system that includes warnings about extreme weather such as tornadoes and hurricanes .

Some critics of Monday 's alert said it was too vague , offering only a description of the wanted vehicle without further context . But Californians should appreciate that such a notification system exists in times of crisis , wrote columnist Jon Healey in the Los Angeles Times .

`` The fact that the alerts were broadcast indiscriminately to San Diego-area cellphones -LRB- and later , to all California phones capable of receiving text messages , as the alert went statewide -RRB- clearly annoyed a lot of wireless customers , '' he wrote . `` But the alerts ca n't really be targeted if police do n't know where the kidnapper is , and it 's impossible to predict who might be in a position to help . So AMBER has to cast a wide net to have any hope of succeeding .

`` Yes , it might have helped if the message had been less cryptic . But now that we 've all seen one , we should be able to recognize what such alerts are trying to tell us . ''

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Californians were startled awake this week by Amber Alerts on their phones

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The alerts were the first sent statewide in California under a new program

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Some people were annoyed by the alerts , while others cite them for saving lives

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Ethan Anderson , 8 , and sister Hannah Anderson , 16 , were abducted last weekend